Pulse generating receiver for coded carrier signals



June 17, 19 47. F c s ETAL 2,422,231

PULSE GENERATING RECEIVER FOR CODED CARRIER SIGNALS Filed Dec. 6, 1944mvzmons ATTORNEY Patented June 17, 1947 PULSE GENERATING RECEIVER FORCODED CARRIER SIGNALS Joseph M. Francis and Allan B. Armist ead,Roanoke, Va., assignors to The Union Switch and Signal Company,Swissvale, Pa., a corporation of Pennsylvania Application December 6,1944, Serial No. 566,820

8 Claims. 1 Our invention relates to signaling apparatus, and moreparticularly to apparatus for receiving coded current.

In the reception of coded current the distortion and attenuation of thecode pulses due to variations of the transmitting medium may adverselyaffect the operation of the decoding unit which usually includes a codefollowing relayand the code may be not properly interpreted. Forexample, in printing telegraph systems distortion and attenuation of'thecode pulses occurs because of variations in the line circuit due tovariations in Weather conditions, such as rain and sleet. Suchdistortion may cause the code following relay to fail to follow the codeand the code message or signal is not correctly reproduced. Because ofsuch distortion the length of the line circuit must be limited to thatthrough which satisfactory reception can be accomplished under allconditions of transmission. This means that repeaters and similarfacilities must be provided for relatively long circuits and whentransmission is difiicult.

Accordingly, a feature of our invention is the provision of signalingapparatus incorporating novel and improved means to receive codedcurrent.

Another feature of our invention is the provision of an improved methodof reception of coded current which is subject to distortion to effect asubstantially uniform energization of a code responsive deviceirrespective of such dis-- tortion of the received current.

Again, a feature of our invention is the provision of improved receivingapparatus to effect substantially uniform energization of a codefollowing or controlling relay over relatively large variations ofreceived energy.

Still another feature of our invention is the provision of signalingapparatus incorporating novel means for locally generating oscillationsin step with the coded current and which oscillations are ofsubstantially uniform amplitude irrespective of the amplitude of thecoded current.

A specific feature of Our invention is the provision of high speedprinting telegraph apparatus incorporating novel means for triggering a,relax ation oscillator by a carrier telegraph current and for operatinga telegraph printer or recorder by the generated oscillations.

Other features, objects and advantages of our invention will appear asthe specification progrosses.

We attain the foregoing features, objects and advantages of ourinvention by utilizing the properties of a controlled ionization byutilizing the properties of a controlled ionization or gas tube whichallows it to oscillate as a relaxation oscillator if the anode voltageis applied through a resistor of such value as to cause the voltage ofthe tube anode to drop below the critical firing voltage when the tubeconducts. The tube is normally biased to a non-conductive condition andis fired when a control voltage is applied to a control electrode of thetube to opposethe normal bias. Since the tube ceases to conduct at theend of each operation cycle, the tube functions as an oscillator as longas the control voltage is applied and ceases to oscillate when thecontrol voltage is interrupted. Thus on and off code periods of thecontrol voltage are reproduced by corresponding on and off code periodsof the locally generated oscillations. The amplitude of theseoscillations is governed by the proportioning of the anode circuit andis independent of the amplitude of the control voltage, the onlycriterion being that the control voltage is large enough to fire thetube. Consequently, a coded control voltage which may vary in amplitudeover a relatively wide range creates a corresponding code in locallygenerated oscillations of sub stantially uniform amplitude.

By proper proportioning of the parts the operating cycle of the tube,that is, the frequency of the locally generated oscillations, is madeequal to the frequency of the carrier of the control voltage. By suchlocking in of the oscillator with the incoming coded carrier the locallygenerated oscillations are substantially in phase with the carrier andfaithfully reproduce codes of relatively high code rates. Thislocking-in feature although desirable is not essential to satisfactoryoperation of the apparatus.

The locally generated oscillations are used to control a code followingrelay. Preferably the oscillations are rectified and the resultantunidirectional current supplied to a direct current code followingrelay. The generated oscillations may be'first amplified in the usualmanner if a higher energy level for energization of the relay is needed.It is to be seen therefore that substantially uniform energization of acode following relay is obtained irrespective of amplitude variations ofthe control voltage and substantially non-distorted operation of therelay is effected, although code distortions in the incoming code pulsemay exist.

The normal bias of the tube is made just under the critical firingcondition of the tube and a relatively weak or low control voltage, suchas prevails under adverse transmitting conditions is sufiicient to firethe tube. The higher values of the control voltage prevailing under goodtransmitting conditions do not over-energize the code following relay.We have found that a code following relay can be satisfactorily operatedat code speeds up to cycles per second with a tento one amplitudevariation of the control voltage. In othe words, we have found that acode following relay can be satisfactorily oper- 3 ated through arelatively long line circuit, such as, for example, a line circuit ofthe order of 300 miles in length.

We shall describe one form of apparatus embodying our invention andshall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form ofapparatus embodying our invention when used with a printing telegraphsystem. It is to be understood that our invention is not limited toprinting telegraph systems and this one application serves to illustratethe many places Where the apparatus is useful.

Referring to the drawing, the reference characters Ll and L2 designatewires forming the two sides of a transmitting circuit through which acoded carrier current is transmitted from a remote station, transmittingapparatus suitable for supplying such coded current being provided atthis remote station. These two wires Ll and L2 may be the two line wiresof a line circuit, or they may represent a line circuit including onewire and ground or the circuit may be an antenna circuit andtransmission effected through radio principles.

To aid in understanding the invention, we shall assume that the linewires Ll and L2 represent a two wire line circuit and that a carriercurrent is used, the carrier being of the frequency of the order of say5000 cycles per second, and the code being effected by periodicallyinterrupting the carrier current at code rates of 25 to 100 cycles persecond. It is to be noted, of course, that other frequencies can be usedand other code rates provided.

In the case here assumed for illustration, the current is received fromthe line circuit through a filter Fl, which includes a transformer Tland two capacitors ill and ll, this filter being tuned to pass a carriercurrent of 5000 cycles and substantially suppress currents of otherfrequencies.

An electron tube Vl is controlled by the energy received from the linecircuit through the filter Fl. Tube Vl may be any one of several typesand is shown as an indirectly heated tetode gas tube. The filament ofthis tube would be heated in any convenient manner for the tube to beconstantly active. Power for exciting the tube Vl is obtained from abattery Bl. To facilitate the obtaining of desired anode and biasvoltages from battery Bl, a resistance network is connected across thebattery. This network comprises two parallel branches, one of whichbranches includes resistors l2 and I3 in series, and the other of whichbranches includes resistors l4 and I5 in series. The junction terminalof resistors l2 and I3 is connected to the junction terminal ofresistors l4 and IS. The resistors are proportioned so thatpredetermined voltages with respect to the junction terminal areobtained at intermediate terminals of resistors l2 and IS.

The tube Vl is provided with an anode circuit extending from anintermediate terminal l6 of resistor l3 through a resistor l1, anode l8and tube space to cathode IQ of the tube, and to the junction terminal23 of the resistance network. A capacitor Cl is connected between anodel8 and cathode l9 and a control electrode 2! of the tube is alsoconnected to the cathode. A control circuit for the tube includesintermediate terminal 22 of resistor 12, winding 23 of transformer Tl,control electrode 24, cathode "l9 and to the junction terminal of theresistance network. Thus, there is impressed upon the tube, a biasvoltage of a. value predetermined by the position of the intermediateterminal 22, and an anode voltage of a value predetermined by theposition of the intermediate terminal l6. Also, a control voltageobtained from the line circuit through the filter Fl is impressed uponthe control electrode 24. The parts are so proportioned that the normalbias voltage applied to the control electrode 24 biases the tube VI to acondition that the voltage applied to the anode from terminal l6 of theresistance network is insufficient to fire the tube, but that arelatively low control voltage from the line circuit to oppose the biasvoltage and drive the control electrode 24 in a positive directioncauses the tube to be fired. That is, the positive half cycles of thecarrier control voltage received from the line circuit through thefilter Fl fires the tube. The parts are arranged that the carriercontrol voltage received under adverse transmission conditions of theline circuit will be sufficient to fire the tube. This means that theline circuit may be relatively long and the received control voltagestill fire the tube without an excessive high voltage at thetransmitting or remote station.

The resistor ll is made of sufiicient value that the voltage drop acrossthe resistor I! when the tube V-l is conducting reduces the anodevoltage to a value below the critical firing voltage of the tube, andthe tube is deionized and a new firing of 'ie tube must be effected bythe next positive half cycle of the control voltage. Again, thecapacitor Cl, resistor i1 and the voltage of terminal l8 are preselectedso that the tube oscillates at the carrier frequency. That is, theoscillations of the anode circuit are locked in and in phase with thecarrier line circuit current. This last characteristic of the apparatusis not required for proper operation thereof but it improves theoperation and efficiency. It follows that the line circuit currentcauses oscillations of the anode circuit current of tube Vl and whensuch line circuit current is interrupted or ceases the oscillations ofthe anode current immediately cease, with the result the code of theline circuit current is reproduced in the oscillations.

The amplitude of the oscillation generated by tube V1 is the sameirrespective of the amplitude of the received control voltage becausethe amplitude of the anodecircuit current is governed by the circuitelements, and these circuit elements once predetermined they remainconstant.

The anode circuit of tube Vi is coupled to the input side of anamplifier AM through capacitor and resistor 26. Amplifier AM is shownconventionally for the sake of simplicity since its specific structureforms no part of our invention and it may be any one of severalwell-known ampl-ifier arrangements. t is sufficient for this applicationto point out that the oscillations of the anode circuit current of tubeVl are applied to the input terminals of amplifier AM and cause acorresponding oscillating electromotive force to be induced in asecondary winding 21 of an output transformer T2, a primary winding 28of which is included in the output circuit of the amplifier. Theelectromotive force of secondary winding 21 is applied to a codefollowing relay CR through a full wave rectifier 29. Relay CR is adirect current code following relay suitable for relatively high speedoperation. It is to be seen therefore that a pulse of unidirectionalcurrent is supplied to the operating winding of relay CR in step withthe code pulses of the carrier line circuit current.

y Also, the magnitude of the energizing pulse supplied to the codefollowing relay CR is substantially uniform irrespective of variationsin the amplitude of the coded line circuit pulse. Relay CE is used tocontrol any suitable device, and as here shown it governs a telegraphprinter PT through an obvious circuit including contact 30 of the relay.The printer PT is shown conventionally for the sake of simplicitybecause its specific structure forms no part of our invention and it maybe of standard structure.

Normally, that is, when no coded carrier current is present in the linecircuit, the tube VI is nonconductive and relay CR is deenergized andinactive. Also, capacitor Cl is charged at a voltage substantially equalto the anode voltage of tube VI Assuming next that a coded carriercurrent is supplied to the line circuit at the remote station, the firstpositive half cycle of the first code pulse of the line circuit ispassed by filter FI and applied to the control electrode 24 of tube VIto oppose the normal bias voltage applied from terminal 22 of theresistance network, and the tube Vi is fired. Capacitor Cl dischargesthrough the tube and the conduction current from battery Bl creates adrop in voltage across resistor H of such value that the anode voltageof the tube is reduced below the firing value of the tube and the tubeis extinguished during the following negative half cycle of the incomingcarrier current. This action is repeated each cycle of the coded pulseof the carrier current with the result oscillations are generated in theanode circuit as long as the code pulse exists, the oscillationsstarting and stopping in step with the code pulse. These oscillationsare or an amplitude predetermined by the circuit elements of the anodecircuit and by the voltage derived from the intermediate terminal l6 ofthe resistance network. The capacitor C! serves to determine the periodof operation of tube VI and in turn the cycle of the oscillations.Preferably the cycle period of the oscillation is made equal to thecycle period of the carrier current. The anode and bias voltages of thetube are adjusted so that a relatively weak control voltage of a valuejust above the noise energy of the line circuit is suificient to firethe tube. Thus the code of the code pulses transmitted through the linecircuit under adverse transmitting conditions is faithfully reproducedin the locally generated oscillations to the same degree that the codeof code pulses transmitted under the most favorable transmittingcondition is reproduced. Any voltage variation of the battery Bl tendingto vary the operating characteristics of the tube VI canbe compensatedby adjustment of the intermediate terminals It and 22 of the resistancenetwork.

The oscillations thus enerated by the tube Vi are applied to theamplifier AM and a corresponding electromotive force is induced in thesecondary winding 21 of the output transformer T2. The electromotiveforce of the secondary winding 2! is rectified by rectifier 29 andunidirectional current applied to relay CR to energize and operate thatrelay. It is clear that a code pulse of unidirectional current issupplied to the relay in step with the code pulse of the line circuitcurrent and the amplitude of the code pulse supplied to relay CR issubstantially uniform and independent of amplitude variations of theincoming code pulse from the line circuit. It is to be noted that theamplifier AM may not be required and the rectifier 29 connected to theanode circuit of tube VI for operation of the code following relay bythe generated oscillations. Relay CR in turn controls the printer PT atwhich the code of the line circlit current is recorded and printed.

Apparatus such as here disclosed has the advantages that a badlydistorted and attenuated coded current of a line circuit is faithfullydecoded Without the use of expensive repeater facilities. Alsorelatively high speed code rates can be satisfactorily transmitted.

Althoughwe have herein shown and described but one form of signalingapparatus embodying our invention, it is understood that various changesand modifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of our invention.

Having thus described our invention, claim is:

1. In combination, means to receive a coded carrier signaling current,an electron tube of the controlled ionization type, a non-inductiveanode circuit including a current source and a resistor connected acrossan anode and cathode of said tube but normally ineffective to fire thetube, said receiving means connected to a control electrode of the tubeto fire the tube in response to each positive half cycle of said carriercurrent, a capacitor connected across said anode and cathode tocooperate with said non-inductive anode circuit to extinguish the tubewhereby oscillations coded according to the code of the carrier currentare created in said anode circuit, and decoding means coupled to saidanode circuit excited by said oscillations to interpret the code iusformed by the oscillations.

In combination, means to receive a carrier current coded according to agiven signal, a controlled ionization electron tube, a non-inductiveanode circuit including a power source and a resistor connected acrossan anode and cathode of said tube but normally inefiective to fire thetube, said resistor proportioned to reduce the anode voltage below thecritical firing voltage of the tube when the tube is conducting, acapacitor connected to said anode circuit to govern the operating cycleof the tube, said receiving means connected to a control electrode ofthe tube to fire the tube each positive half cycle of said carriercurrent to generate in said anode circuit oscillations substantiall inphase with said carrier current to provide oscillations of the anodecircuit current coded according to said given signal, and decoding meanscoupled to said anode circuit excited by said oscillations to reproducesaid signal.

3. In receiving apparatus for receiving from a transmitting medium acarrier current which has been coded to convey a signal, the combinationcomprising; a gas tube having an anode, a cathode and at least onecontrol electrode; a source of direct current connected across saidanode and cathode, through a resistor to form a non-induc tive anodecircuit, said current source normally ineifective to fire the tube, saidresistor of a value that its voltage drop reduces the anode voltagebelow the voltage required to maintain the tube fired when the tube isconducting, said transmitting medium coupled to said control electrodeand cathode to fire the tube each positive half cycle of said carriercurrent to generate oscillations coded according to the signal conveyedby the carrier current, and decoding means including a rectifier and arelay coupled to said anode circuit to opwhat we erate said relayaccording to the coding of said oscillations.

i. In receiving apparatus for receiving from a line circuit a carriercurrent of a given frequency and coded at a preselected code, thecombination comprising; a gas tube having an anode, a cathode and atleast one control electrode; a source of direct current, a resistor, ananode circuit including said direct current source and resistorconnected to said anode and cathode but normally ineffective to fire thetube, said anode circuit being substantially non-inductive said resistorproportioned to reduce the anode voltage below that required to maintainthe tube ionized when the tube is conducting, a capacitor connectedacross said anode and cathode to govern the operating cycle of saidtube, said line circuit connected to said control electrode and cathodeto fire the tube each positive half cycle of said carrier current tocreate in said anode circuit oscillations coded at said preselectedcode, and means including a rectifier and a relay coupled to said anodecircuit to operate said relay according to said preselected code due tothe coding of said oscillations.

5. In combination; a gas tube having an anode, a cathode and a first anda second control electrode; a source of power and a resistor in seriesconnected across said anode and cathode, said resistor ol a value thatits voltage drop reduces the anode voltage below that required tomaintain the tube conductive when the tube is conducting, a capacitorconnected across said anode and cathode and having connection to saidsecond control electrode to govern the operation cycle of the tube,means including a bias voltage source and a winding connected to said fist control electrode and cathode to bias the tube to be normallynon-conductive, transmitting means coupled to said winding to supply attimes a carrier voltage coded to convey a given signal, said carriervoltage of an amplitude sufficient for each positive half cycle to firethe tube for generating in the anode circuit oscillations codedaccording to said given signal and of substantially uniform amplitudedue to the proportioning of said anode circuit, and decoding meansincluding a rectifier and a relay coupled to said anode circuit througha capacitor to operate the relay according to the coding of saidoscillations free from distortion due to the uniform amplitude of theoscillations.

6. In receiving apparatus for receiving a carrier current coded atdifferent preselected codes, the combination comprising; a gas tubehaving an anode, a cathode and at least one control electrode; a sourceof direct voltage and a resistor in series connected to said anode andcathode to form a non-inductive anode circuit, a capacitor connectedacross said anode and cathode, a receiving element and a bias voltagesource in series connected to said control electrode and cathode to forma control circuit, said bias voltage source to bias the tube to benormally extinguished and to be fired in response to a preselectedpositive voltage, means to at times supply said coded carrier current tosaid receiving element to fire the tube each positive half cycle of thecarrier, said capacitor and anode circuit to extinguish the tube eachnegative half cycle of the carrier to create oscillations in the anodecircuit, said oscillations being in phase with said carrier and ofrelatively large amplitude due to said non-inductive anode circuit andbeing coded according to the code of the carrie due to action oi thetube, a code i'ollowing relay, and circuit means coupled to said anodecircuit to supply to said relay energy corresponding to the coding ofsaid oscillations.

7. In receiving apparatus for receiving a carrier current of a givenfrequency and coded at a preselected code, the combination comprising; agas tube having an anode, a cathode and at least one control electrode;a source of direct voltage and a resistor in series connected acrosssaid anode and cathode to form a non-inductive anode circuit, acapacitor connected across said anode and cathode, a bias voltagesource, a filter in series with said bias voltage source connectedacross said control electrode and cathode to form a control circuit,said bias voltage to maintain said tube deionized, means connected tosaid filter to supply at times said coded carrier current to saidcontrol circuit, said filter tuned to pass current of said givenfrequency, said bias voltage source proportioned for each positive halfcycle of said carrier to ionize said tube, said capacitor and resistorproportioned to deionize said tube each negative half cycle of saidcarrier whereby oscillations of said given frequency and code arecreated in said anode circuit, a code following relay, and circuit meansto couple said relay to said anode circuit to operthe relay in step withsaid code due to the 3 ons thus created in said anode circuit.

8. In receiving apparatus for receiving from a line circuit a carriercurrent of a given frequency and coded at a preselected code, thecombination comprising; a gas tube having an anode, a cathode and atleast one control electrode; a source of direct current, a first and asecond resistor in series connected across said source, each said firstand second resistors having an adjustable intermediate terminal and thejunction terminal of the resistors being connected to said cathode,third resistor connected between said anode and the adjustable terminalof said first resistor to form an anode circuit for the tube, acapacitor connected across said anode and cathode, means includingfilter to connect said line circuit between said control electrode andthe adjustable terminal of said second resistor to form a controlcircuit for the tube, said filter tuned to pass current of said givencarrier frequency and said adjustable terminal of the second resistorset to bias the tube to maintain the tube normally non-conductive and tobe fired in response to a relatively low voltage of the carrier passedby the filter, said third resistor and capacitor to cause the tube tofunction as a relaxation oscillator to create oscillations through saidthird resistor of said given carrier frequency and which oscillationsare coded according to the code of the line circuit current, and. a codefollowing relay coupled to said anode circuit through a capacitor tooperate the relay according to the coding of said oscillations.

JOSEPH M. FRANCIS. ALLAN B. ARMISTEAD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PAIENIS Number Name Date 2,018,102 Watts Oct. 22, 19352,197,414 Place Apr. 16, 1940 2,096,982 Schlesinger Oct. 26, 19371,642,861 Turner Sept. 20, 1927

